1. Field of the Invention
The present invention relates to a parallel cold shield for reducing undesirable background radiation from reaching detectors so as to enhance the detector response to radiation within its intended field of view. More particularly, the invention relates to a cold shield for a tiltable array of infrared detectors whose sensitivity decreases with the amount of background radiation received but which receive radiation from any of a plurality of directions.
2. Description of the Prior Art
Cold shields for use in limiting background radiation for infrared detector arrays are common in the prior art. For example, in U.S. Pat. No. 3,963,926 to Sebastian R. Borrello issued June 15, 1976, a thermal energy receiver is disclosed which employs a cold shield through which apertures for each detector are formed. The detectors only receive energy generated within a solid angle subtended by the optical elements. A difficulty encountered in the Borrello patent was that the cold shield had limited effectiveness in high density two-dimensional arrays common in modern day infrared systems. In the William J. White U.S. Pat. No. 4,576,679 issued Mar. 18, 1986, and assigned to the assignee of the present invention, a shield which overcomes that problem in the Borrello patent is disclosed involving etching of glass apertures and positioning the aperture edges in a predetermined relationship with the edges of the detectors to thereby shield the detectors from radiation generated outside the field of view of the optical system.
Both the Borrello and White disclosures have the difficulty that the shield and detector array need to be in a predetermined positional relationship, generally perpendicular, to the optic axis of the field of view. If the array were to be tilted with respect to the optical axis, an edge of the cold shield would cut off part of the desired field of view and the effectiveness of the array would be diminished. This difficulty arises in the prior art because the cold shield has been an individual aperture located just above each of the detectors and of a shape such that energy can be received on the detectors only from a predetermined cone of view. Thus, when the array is tilted at least one edge of the aperture moves into the cone of view and begins blocking radiation the detector should receive for best sensitivity.